[Update] Infinity Ward is close to releasing an update that will address many of the issues people are having with the XBOX Live gameplay. http://forums.xbox.com/2598446/ShowPost.aspx Also, apparently, every XBOX 360, has 64 MB of memory on board that can be used for downloadable content or patches/updates. It's a very limiting amount of memory but usable.
Now that I've had my XBOX 360 for a little over a week, I find myself playing Call of Duty 2 the most. I like sports games a lot, but I just haven't been enjoying the game play as much on the current 360 sports games as I have with the older XBOX games.
I fully expect that to change, the game developers need time with the new XBOX 360 hardware. If you remember, XBOX games continually got better over time as the game developers got accustomed to the hardware and built up libraries of code they could reuse allowing them to spend more time focused on other aspects of the game.
The other night, a few of us from work planned an XBOX Live session to play Call of Duty 2. We found we couldn't create a private game or host a party. Very surprising. I did a bit of searching, and there have been complaints with the lag and the lack of this support: http://digg.com/gaming/Complaints_grow_with_Call_of_Duty_2_online_for_XBox360
I also found a funny thread on how you can gain some limited control over the session: http://forums.xbox.com/2040758/ShowPost.aspx. Quite a few hoops to jump through and you still can't control who enters (or stays in) the lobby.
I got to hoping that this deficiency might be addressed by some kind of downloadable patch, much like many of the games on the XBOX were fixed/improved in this manner. I then remembered that not all XBOX 360s have hard drives. For content updates, that's ok, the people that don't have hard drives won't get the latest content... but what about patches that fix glitches or close down cheats that people are exploiting? You can't limit people who don't have hard drives from playing on Live, can you?